In recent years, an optical measurement apparatus for examination of a living body has been developed, by which the functions of tissue in a living body are observed by transmitting laser light to the interior of the living body and detecting signals generated due to interaction between the laser light and hemoglobin in the blood flow within the living body. Such an optical measurement apparatus for the living body is disclosed, for example, in Japanese Patent Laid-open Publication JP-A-9-98972 (hereinafter referred to as “document 1”).
The optical measurement apparatus for the living body, as mentioned in the above-reference patent publication, is constituted of modulated semiconductor laser devices for generating light having various modulation frequencies; light-transmitting optical fibers for guiding the light generated by the semiconductor laser devices to transmit light to a plurality of positions; detecting optical fibers for collecting the light which has passed through the living body (hereinafter referred to as “living-body transillumination”) and for guiding it to photodiodes; a fixing member for fixing the tips of the light-transmitting optical fibers and the detecting optical fibers to predetermined positions on the living body; lock-in amplifiers for separating electrical signals of the optical intensity of the living-body transillumination which are output from the photodiodes (hereinafter referred to as “living-body transillumination intensity signals”), according to wavelength and measurement position; an A/D converter for converting the outputs of the lock-in amplifiers into digital signals; an input/output unit having an image generation unit for generating an image of the living-body transillumination intensity signal (a topography image), corresponding to variations of hemoglobin concentration at each measuring point from the living-body transillumination intensity signals, after A/D conversion; and an image display unit for inputting an operation instruction for the apparatus and displaying the living-body transillumination intensity signal image.
In this specification, the term “transillumination” hereinafter means any kind of light, including transmitted light, reflected light, and scattered light, which is generated at a light source and detected at a detector (a light detector) after interacting with the living body.
In a measurement using the conventional optical measurement apparatus for the living body as described above, the fixing member is first placed on the living body, and the light-transmitting optical fibers and the detecting optical fibers, supported by a probe holder provided to the fixing member, are applied to predetermined positions on the living body. Then, in a preliminary measurement, for example, plural measurements of 10 seconds each, living-body transillumination intensity signals in the resting state are measured, and the measured values are averaged to calculate hemoglobin concentration in measured areas of the living body in the resting state. Next, the living-body transillumination intensity signals are measured in the state where stimulation is applied to the living body.
Then, relative variations of oxygenated hemoglobin concentration and relative variations of deoxygenated hemoglobin concentration are calculated at each measuring point from the measured living-body transillumination intensity signals in the resting state and the measured living-body transillumination intensity signals in the state where stimulation is applied. An image of the living-body transillumination intensity signal is generated from the relative variations of oxygenated hemoglobin concentration, the relative variations of deoxygenated hemoglobin concentration, and the relative variations of total hemoglobin concentration, which is the sum of the relative variations of oxygenated hemoglobin concentration and deoxygenated hemoglobin concentration, and this image is displayed.
To describe in more detail the mode of image display in the conventional optical measurement apparatus for living body, relative variations of oxygenated hemoglobin concentration, relative variations of deoxygenated hemoglobin concentration, and relative variations of the total hemoglobin concentration are calculated at each measuring point from the living-body transillumination intensity signal acquired at a measuring point (a position to be measured), which is the area between a pair of elements, consisting of the light-transmitting optical fiber and the detecting optical fiber, which are adjacently placed. The relative variations of oxygenated hemoglobin concentration and the relative variations of deoxygenated hemoglobin for each pixel are calculated by spline interpolation, and the like, from the relative variations of oxygenated hemoglobin concentration and the relative variations of deoxygenated hemoglobin concentration obtained at each measuring point. When the result thereof is displayed as an image, the area where the variation is minimum, among those relative variations, is provided with blue hue, the area where the variation is maximum is provided with red hue, and areas between them are provided with medium hues between blue and red in accordance with their variation. The area where the variation of hemoglobin concentration is maximum represents the area which has been activated by the application of stimulation. In this manner, the area which has been activated by stimulation, that is, the functioning area of the living body, is identified by the variations of hemoglobin concentration in the measuring area.
After considering the above-described conventional technique, the present inventor has found a problem. That is, to take the therapy of epilepsy as an example, therapy in which the focal point of epilepsy is identified and is excised requires not only accurate identification of the focal point of epilepsy, but also accurate identification of positions of a speech function area (the “speech area”), a visual function area (“the optic area”) and the like. The reason for this is to enable execution of the focal point of epilepsy to a maximum, while reducing the damage to the speech area and the visual area to a minimum, by accurately identifying the position of the speech area and the visual area, thus to improve the treatment outcome.
On the other hand, to accurately identify the areas where the relative variations of hemoglobin concentration greatly changes (the focal point of epilepsy), it is necessary to identify the measuring point having the largest relative variations of hemoglobin concentration and the areas around it having large relative variations. However, when the relative variations of hemoglobin concentration are displayed with colors, as in the conventional optical measurement apparatus for a living body, the area to be examined might depend on the difference in the examiner's sensitivity to colors. Therefore, the provision of a display method by which the examiner can objectively identify the area where the relative variation of hemoglobin concentration is greatest has been desired.
An object of the present invention is to provide a technique by which the examiner can objectively identify the area to be examined in diagnosis using an optical measurement apparatus for a living body.
Another object of the present invention is to provide a technique by which the efficiency of diagnosis using an optical measurement apparatus for a living body can be improved.
The above-described and other objects and novel features of the invention will be revealed in the description provided in this specification and from the attached drawings.